Algae use light and carbon dioxide for growing and this process generates oxygen. Normally algae are produced in open ponds, transparent piping systems, submerged plastic bags, etc.
The disadvantages of these systems are the amount of energy necessary for mixing, feeding the carbon source and removal of the generated oxygen. Also the amount of water evaporation, heating of the water in daytime and the cooling in the night is a problem. This is because the only sensible source of light for growing algae is sunlight, which is in principle available for free, but for optimum growth, the algae require a high influx of light. However, sites where high sunlight input is available are almost inherently hampered by being located in arid zones of the earth, where water, also necessary for algal production, is very scarce.
These disadvantages limit the algae concentration in the reactor systems and increase thus the amount of reactor space necessary for a specific amount of algae production. Thus there is need for more efficacious and up-scalable reactor vessels for growing photosynthetic microorganisms with improved light supply.
JP-A 2000-300244 discloses a photosynthetic culturing device having light-transmitting plates made of acrylic, which are arranged vertically in a reactor, the (sun)light entering on the top of the reactor. The distance of 10-70 mm between the plates provides the reactor space containing the culture medium in an up-flow arrangement. The top ends of the spaces between the plates are closed with covers (“first invention”) or with triangular extensions of the acrylic plates for increased irradiation surface (“second invention”). The light-transmitting plates may have light-scattering surfaces provided by unidirectional striping, and pairs of plates may be formed in such a way that the light-scattering surfaces are at the inner side of the pairs, as described in JP-A H08-262232.
The reactors of the types descried in JP-A 2000-300244 and JP-A HOS-262232 do not provide for optimum irradiation efficiency and algal production rates. Moreover, the arrangement nature of the plates used according to this prior art do not allow the provision of robust, large scale photosynthesis reactors for use at remote sites and requiring minimum maintenance operations.